Drive axle assemblies traditionally include a differential gear assembly that allows speed differentiation between a pair of shafts. For example, the use of the differential gear assembly in a traditional drive axle configuration allows an outer wheel end to rotate at a faster speed than an inner wheel end as a vehicle negotiates through a turning maneuver. The differential gear assembly includes a first side gear, a second side gear, and a plurality of differential pinion gears that are in meshing engagement with the first and second side gears. The first and second side gears and differential pinion gears interact with each other to provide shaft speed differentiation as needed.
Differential gear assemblies can be used in single drive axles and tandem drive axles. In either type of axle, each of the side gears is coupled to a shaft. In a single drive axle configuration, each side gear is coupled to an axle shaft with each axle shaft driving a wheel end. A tandem drive axle includes a forward-rear axle and a rear-rear axle that is coupled to the forward-rear axle with a connecting driveshaft. In a tandem drive axle configuration, the forward-rear axle and the rear-rear axle each include a differential gear assembly that drives a respective pair of axle shafts.
A tandem drive axle also includes an inter-axle differential gear assembly that allows speed differentiation between the forward-rear and rear-rear axles. The inter-axle differential gear assembly provides speed differentiation between driving input to the differential gear assembly for the forward-rear axle and driving input to the differential gear assembly for the rear-rear axle as needed. The first side gear in an inter-axle differential gear assembly is supported by a driving input shaft and the second side gear is coupled to a thru-shaft. The thru-shaft provides driving output from the forward-rear axle, which drives the connecting driveshaft, which in turn provides driving input to the differential gear assembly of the rear-rear axle.
In either configuration, it is important to properly lubricate gear teeth contact surfaces between the differential pinion gears and the first and second side gears. If an inadequate amount of lubricating fluid is provided, overheating can occur, which can significantly increase gear tooth wear or can lead to premature gear failures.
Proper lubrication takes on even greater importance for an inter-axle differential gear assembly. Due to the unique configuration of the tandem drive axle, inter-axle differential components are susceptible to torsional driveline vibrations. These torsional driveline vibrations can cause gear teeth to flatten at contact lines between mating gear teeth. This flattening problem has an increased occurrence at the second side gear of the inter-axle differential gear assembly.
One solution has been to supply the tandem drive axle with a separate pumping mechanism, such as a gerotor pump lubrication system, for example. This gerotor pump lubrication system is also typically required for inter-axle differential spinout protection. However, the addition of a separate pumping mechanism increases component and assembly costs, and adds complexity to the tandem drive axle.
It would be beneficial to provide a simplified method and apparatus for properly lubricating a differential gear assembly without requiring installation of a separate pumping mechanism. The method and apparatus should be easily incorporated into existing axle designs, as well as overcoming the other above-mentioned deficiencies with existing axle designs.